The present invention relates to a mixing device that provides a frothy fluid product. More particularly, the invention relates to a mixing device for mixing, frothing, and dispensing a beverage, and to a method for providing a frothy fluid product.
Espresso and other coffee and milk drinks are often prepared by mixing a powder in water. Traditionally, a milk froth is provided to the drink by steam frothing.
Mixing devices are known for speedier preparation of such beverages and other foods by mixing a powdered food component with a liquid, such as water. These devices typically feed the powdered component into the water, which is often pumped tangentially into a mixing chamber to create a whirlpool to mix the powder into the water. The mixture is then fed to a whipping mechanism, which is usually a rotating plate. The plate aerates the mixture and produces a froth. The frothed mixture is usually dispensed into a container for drinking.
U.S. Pat. No. 5,927,553, for example, discloses a mixing and dispensing apparatus with a cruciform frothing blade. Other shapes of frothing blades are also known. For instance, companies such as Rhea and Zanussi use whippers with an axially short disk with very steep sloped walls. Other whippers have rotors with independent ramps extending from a substantially flat plate. The known devices generally have their greatest efficiency for preparing a small group of products.
There is a need for a mixing device with an improved frothing effect and efficiency. The present invention satisfies this need.
The invention relates to a mixing device with high versatility, as it is able to very effectively aerate and froth different products, such as coffee and milk products, for serving in a cup. A preferred embodiment of the device has an input container configured for receiving a product that comprises a fluid component and a second component. A whipper is provided in a housing of the device with a conical whipper surface that has an axis and that is configured for aerating and frothing the product. The whipper surface extends between first and second end portions of the whipper. The first end portion has a first diameter and is in fluid communication with the input container to receive the product. The second end portion is disposed downstream of the first end portion and has a second diameter that is larger than the first diameter. The whipper surface of this embodiment is oriented at an angle to the axis of about between 5xc2x0 and 65xc2x0, more preferably about between 10xc2x0 and 45xc2x0, and most preferably about between 15xc2x0 and 35xc2x0. A controlled shear gap is defined between the whipper surface and the housing to provide a sufficient flow rate and energy transfer to the mixture for a desired foaming effect. The perpendicular shear gap has a width of about between 0.4 to 1.1 mm. A motor is in driving association with the whipper for rotating the whipper about the axis at a speed sufficient for aerating and frothing the product. Additionally, a product exit conduit disposed downstream of the whipper and configured for dispensing the product of the fluid and second components.
In the preferred embodiment the second diameter of the whipper rotor is at least about 10% larger than the first diameter. More preferably, the second diameter is between about 1.25 and 2.5 times the size of the first diameter. The preferred axial length of the whipper surface about between a quarter and twice the size of the first diameter.
Also, the motor and whipper of the preferred embodiment are configured for providing an energy dissipation to the product of about between 1 J/g and 2.5 J/g with a product flow rate of about between 5 g/sec and 30 g/sec. The energy dissipation is preferably selectively in at least the range of about 0.5 J/g to 1.5 J/g with a product flow rate of about between 5 g/sec and 30 g/sec.
The conical surface of this embodiment has a substantially constant surface angle between the first and second end portions, but the surface angle can vary along the length of the whipper surface. A whipper housing preferably has a shape corresponding to the whipper surface. In addition, the whipper surface of one embodiment defines grooves extending between the first and second ends.
To obtain the frothing effect desired, and depending on the mixture of components fed into the device, a preferred motor controller is configured for selective operation at various speeds. In one embodiment, the motor controller is configured for varying the rotation speed of the motor between first and second speeds during the production of a single product.
A first wall member is preferably disposed downstream of and facing the second end of the whipper in a preferred embodiment. The first wall member is spaced from the second end by about between 0.25 mm and 5 mm, and more preferably by about between 1 mm and 3 mm. In the preferred embodiment, the first wall member includes at least one rib extending radially with respect to the axis and protruding towards the whipper and configured for increasing the efficiency of the frothing of the product. Preferably, a plurality of ribs is provided, and more preferably, there are between two and eight ribs to increase efficiency in frothing. The preferred height of the ribs from the back wall of the wall member is about between 0.5 mm and 4 mm, and preferably the ribs are spaced from the second end by about between 0.25 mm and 5 mm. The back wall itself is preferably sloped away from the whipper in a radially outward direction to improve the outwards radial flow of the product.
The preferred embodiment includes a support member configured for supporting the input container. The support member may include a mounting member attachable to a support wall or other support element. The support member also preferably includes a second bayonet attachment portion configured for releasably engaging a first bayonet attachment portion of the input container to attach the input container to the support member. Preferably, one of the bayonet attachment portions comprises a cam ramp, and the other comprises a latch. A resilient member is preferably associated with the input container and support member for biasing the input container away from the support member when the bayonet attachments are released from each other to facilitate the separation of these parts. This arrangement allows easy removal and replacement of the input container for clearing.
To prepare a beverage, a user preferably introduces milk powder and a diluent into a shear gap defined adjacent a tapered whipper surface that has an axis and that extends between first and second surface ends. The first surface end in this preferred method has a first diameter of at least about 18 mm, and the second surface end is disposed downstream of the first surface end and has a second diameter that is larger than the first diameter. The whipper surface is oriented at a surface angle to the axis of less than 90xc2x0 to extend the whipping surface with a sufficient length and surface area to provide a high frothing efficiency. The whipper is rotated to mix, aerate, and froth the milk powder and diluent to produce a frothed beverage having a ratio of froth volume to liquid volume of at least about 60%. The milk powder may comprise, for example, a medium heat milk powder, preferably a skim milk powder.